Control system



May 20, 1941. R w, STAGGS v 2,242,897

CONTROL SYSTEM Filed June 30, 1939 WITNESSES:

- INVENTOR- lussel/ W. 517995.

Patented May 20, 1941 CONTROL SYSTEM Russell W. Staggs, Detroit, Mich.,assignor to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application June 30,1939, Serial No. 282,175

12 Claims.

My invention relates to control systems and it has particular relationto control systems utilizing electric discharge apparatus forcontrolling the flow of power from a source to a work circuit.

An object of my invention is to provide a system of simple structureincorporating a minimum of auxiliary discharge devices for controllingthe current flow through a pair of main electric dis charge devices.

Another object of my invention is to provide a system of simplestructure incorporating a minimum of auxiliary discharge devices forcontrolling current flow through a pair of main electric dischargedevices of the immersed ignition electrode type connected inanti-parallel.

A more general object of my invention is to provide a novel circuit forcontrolling an electric discharge device of the immersed ignitionelectrode type.

A further object of my invention is to provide a simple, efiicient, andinexpensive system for controlling the current flow from a source to aload.

An ancillary object of my invention is to provide a resistance, spot andseam welding system of simple construction that shall operate reliablyand efiiciently.

In accordance with my invention, power is supplied to the material to bewelded, or to any other suitable load from .an alternating-currentsource through electric discharge devices of the arc-like type. The maindischarge devices are controlled by an auxiliary discharge device of thearc-like type. When the latter is rendered conductive, current flowsthrough the main discharge devices and the load, and when the auxiliarydischarge device is non-conductive, the current flow through the maindischarge devices is interrupted.

The auxiliary discharge device is rendered conductive by the applicationof energizing potential in its control circuit. It is renderednon-conductive by the application in its control circuit of a potentialcounteracting the energizing potential.

The control system for the pair of electric discharge devices of theimmersed ignition electrode type connected in anti-parallel issimplified, in accordance with my invention, by interconnecting theignition electrodes of the discharge devices through a high impedancenetwork made up of, relatively low impedance elements, and supplyingignition current to the discharge devices through the low impedanceelements. In particular, the ignition electrodes are interconnected by anetwork comprising a plurality of rectifiers arranged for full waverectification. To supply ignition current, the impedance of the networkis controlled by means of the auxiliary discharge device referred tohereinabove.

Finally, I provide an auxiliary relay which opens the circuit for theauxiiiary discharge device after each welding interval and reestablishesthe control circuit to its initial condition. To initiate the flow ofWelding current, a closing coil of the relay is connected across thesource. Simultaneously with the initiation of the flow of weldingcurrent, a holding coil of the relay which is connected directly acrossthe Welding load becomes energized to maintain the relay in the closedposition. When the main discharge devices are rendered non-conductive,the holding coil becomes deenergized and the relay is actuated to theopen position. The relay remains in the open position until theinitiation of a new welding operation.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional object and advantages thereof, willbest be understood from the following description of a specificembodiment when read in connection with the accompanying drawing, thesole figure of which is a diagrammatic view of an embodiment of myinvention.

The apparatus shown in the drawing comprises a load welding transformer3, to the terminals of the secondary 5 of which a pair of weldingelectrodes 1 are connected. The electrodes engage the material 9 to bewelded and when current is transmitted through a primary ll of thetransformer, welding current fiows through the material. If desired, adischarge resistor 2 may be connected across the primary winding l I sothat a more rapid decay of transformer flux will result when thecircuit, through the Welding electrode l, is opened.

The primary ll of the transformer is supplied from analternating-current source i3, which may be of the usual GO-cyclecommercial type, through a pair of electric discharge devices I5 and I6connected in anti-parallel. The discharge devices are of the immersedignition electrode type. The discharge device I5 has an anode ll, amercury pool cathode I 9, and an ignition electrode 2|. Similarly, thedischarge device l6 has an anode I8, mercury pool cathode 20 and anignition electrode 22. If desired, (although such is not necessary tooperativeness), a rectifier 23, preferably of the dry type, may beconnected between the starting electrode 2! and the cathode l9, and

similarly, a rectifier 25 may be connected between starting electrode 22and cathode 259. For example, if the characteristics of the startingelectrodes 2i and 22 are different, rectifiers 23 and 24 may be utilizedto shunt part or all of the starting electrode current during apredetermined portion of the cycle of, the alternating current.

The ignition electrodes 2i and 22 of the discharge devices areinterconnected by a network 25 arranged as a conventional full waverectifier bridge circuit comprising a plurality of rectifiers 23, 2?, 28and 25. The network is arrang d to convert the alternating current fromthe source through the ignition electrodes into a unidirectional currentfor control purposes. While the rectifiers 25, 21, 28 and 29 arepreferably of the dry type, it will be understood that rectifiers of theelectronic or gaseous discharge type may be utilized.

To control the flow of ignition current, an auxiliary discharge deviceSi is provided. The lat er is preferably of the arc-like type andcomprises an anode 33, a hot cathode 35, and a control electrode 3'1 anda gaseous medium at a suitable pressure. The cathode 35 of the auxiliarydischarge device 3| is connected to the junction of rectifiers 25 and2i. The anode 33 of the auxiliary discharge devices is connected to thejunction of rectifiers 28 and 29. The cathode 35 may be energized by atransformer 38 or any other suitable means.

To control the energization of the aux iary discharge device 3l, controlpotential is impressed between the control electrode and the cathode bymeans of a timer. The timing means comprises a full wave rectifier 39energized by source it through a transformer 43, or any other suitablesource of potential and a capacitor ll connected in series between thecontrol electrode 37 and the cathode 35. A source of unidirectionalpotential comprising a full wave rectifier 33, which may be energizedfrom source i3 through a transformer 44, and potentiometer is connectedacross capacitor 4| through an adjustable resistor 41. Rectifiers 39 and43 may be of the dry copper-copper oxide type. An electro-magneticdevice or a relay 9 having a closing coil i, a holding coil 3, and aplurality of contact members 55, 51 and 59 is also provided. It will beunderstood that conventional starters or timers, many of which are wellknown in the art, may be utilized for controlling the auxiliarydischarge device 3|.

To initiate a welding operation, a circuit controller 6| which ispreferably manually operated and may be a foot switch or a pushbutton,is closed to thus energize closing coil 5i and actuate relay 49 to thusopen the circuit through contact members 51 and close the circuitthrough contact members 55 and 59. The closing of lower contact membersof relay completes the circuit across the network through the auxiliarydischarge device ?ii. Because of the positive pctential impressed oncontrol electrode 3? by the source 33, the auxiliary discharge device isrendered conductive.

Assume that at the instant under consideration, the polarity of thesource 13 is such that the anode. ll of the left-hand discharge devicel5 and the cathode 25 of the right discharge device |6 are positiverelative to the cathode ii) of the left-hand discharge device and theanode it of the right-hand discharge device. Ignition current will thenflow through a circuit which extends from the energized cathode 28through ignition electrode 22, rectifier 23, contact members 55 of relayd9, anode and cathode of auxiliary discharge device iii, rectifier 26,ignition electrode 2! to the energized cathode it. This ignition currentcauses discharge device it to be rendered conductive and current to flowfrom source it through the left-hand discharge device 55 and primary iiof the welding transformer 3. Current does not flow through theright-hand discharge device because at this time, its anode i3 isnegative relative to its cathode Holding coil 53 connected parallel onewhich may be connected in series with primary winding I I also becomesenergized thus maintaining the relay id in the closed position. Closingcoil 5i becomes deenergized as soon as switch Eli is released.

It will be understood that the holding coil may be omitted from relay idand a holding cir-- cult may be established by connecting conductor 63to the junction of switch iii and closing coil 5i. It will also beunderstood that closing coil 51 may be omitted from relay and utilizedto actuate a second relay having two of normally open contact members,one set connected in parallel with contact members and the second setconnected in parallel with contact members 59.

When the potential of the source it reverses, the ignition current flowsfrom energized cathode l9 through control electrode 2i, rectifier 23,contact members 55, auxiliary discharge device 3i, rectifier 2i andcontrol electrode 22 to energized cathode 23. However, at this time, theanode potential of the right-hand discharge device it is positive andthe latter is rendered conductive, while the left-hand discharge deviceis not conductive. It is to be noted that as soon as one or the other ofthe main discharge devices id or it is rendered conductive and thisoccurs immediately after the initiation of current fie-w through theassociated electrodes, the network and auxiliary discharge device 3! areshort circuited by the main discharge device and the current flowthrough the ignition electrodes 2i and 22 is discontinued for theremainder of the half cycle. In this manner, power loss and the otherdisadvantages arising from the continuous current flow through theignition electrodes, is avoided.

The opening of contact members opens the circuit shunting the dischargedcapacitor ii. The closing of the upper contact members 51- completes thecircuit for energizing potentiometer 25, thus the capacitor M isgradually charged through adjustable resistor and a negative bias isimpressed in the circuit of control electrode 31 to counter ct thepositive potential of rectifier 39. The time required for chargingcapacitor 4! may be varied by changing the setting of the adjustable tapof resistor 41 or by changing the setting of the capacitor a variablecapacitor is utilized. When the resultant potential impressed betweenthe control electrode .and the cathode 35 reaches a predetermined value,the auxiliary discharge device El is ren dered non-conductive. Thusignition current no longer flows through ignition electrodes 25 and 22and network 25. The main discharge devices I?) and it becomenon-conductive and remain non-conductive and the current flow throughthe welding transformer 3 is discontinued. The holding coil 53 of relay49 is now deenergized and relay $9 is actuated to open contact membersand 5t and close contact members The opening of contact members 58 opensthe circuit through potentiometer 45. The closing of contact members 51in parallel with capacitor 4| completes the circuit for discharging thecapacitor 4| in preparation for the next cycle of operation. The openingof contact members 55 prevents the auxiliary discharge device 3| frombeing rendered conductive until the next cycle of operation is initiatedby the closing of switch 6|,

Should it be desirable to automatically reinitiate the cycle ofoperation after a predetermined time, a second timer, (such as, forexample, timer B shown in Fig. 149 on page 128 of Industrial Electronicsby F. H. Gulliksen and E. H. Vedder) may be utilized. The primarywinding of the transformer of timer B may be connected across the sourcel3, the contact members of relay 3, which open a circuit when theoperating coil of relay 3 is deenergized, are connected in series withswitch 8| and closing coil 5|, and contact members of relay 4 connectedin the circuit of timer B may be actuated by relay 49. The timing meansfor auxiliary discharge device 3| is adjusted to give the proper weldregardless of operating speed. The second timer is then adjusted to givethe operator the required time to move the work. Each timer isadjustable independently of the other. The operation of the systemcontinues so long as switch 6| is closed.

Furthermore, it will be understood that the control system may beutilized for seam welding by employing a suitable timer, such as thetimer utilized in Fig. 7 of the patent to Edwin H. Vedder, No.2,111,013, dated March 15, 1938, and as signed to Westinghouse Electric& Manufacturing Company, in place of the timer shown in the drawing andhereinabove described. The control circuit of this timer may beenergized from source l3. Ihe positive terminal of battery 16 isconnected to cathode 35 of auxiliary discharge device 3| instead of theintermediate tap of resistor 80, and the conductor from the junction ofsecondary winding of transformer 12 and resistor '53 is connected tocontrol electrode 31 of discharge device 3| instead of the intermediatetap of transformer winding I9.

t is to be noted that while the discharge devices |5 and I6 areillustrated as separate valves, they may, under certain circumstances,be replaced by a single double-polarity discharge device comprising apair of mercury pool electrodes in each of which an ignition electrodeis immersed.

I do not wish to be restricted to the specific structural details,arrangements of parts or circuit connections herein set forth, asvarious modifications thereof may be efiected without departing from thespirit and scope of my invention. I desire, therefore, that only suchlimitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. In combination, a pair of electric discharge devices connected inanti-parallel for controlling the supply of power from a source to awork circuit, each discharge device having a plurality of principalelectrodes and an ignition electrode in contact with one of the saidprincipal electrodes, a network connected between the said ignitionelectrodes, the said network comprising a plurality of rectifiers, anauxiliary electric discharge device connected across the said network,control means associated with the said auxiliary discharge device forcontrolling the flow of cur. rent through the said network and therebycontrolling the energization of the said pair of discharge devices.

2. In combination, a pair of electric discharge devices connected inanti-parallel for controlling the supply of power from a source to awork circuit, each discharge device having a plurality of principalelectrodes and a control electrode, a network comprising a plurality ofrectifiers, the said network having a junction connected to one of saidcontrol electrodes and another junction connected to the other of saidcontrol electrodes, an auxiliary electric discharge device connectedacross the said network and control means associated with said auxiliarydischarge device for controlling the flow of current through the saidnetwork and thereby controlling the energization of the said pair ofdischarge devices.

3. In combination, a pair of electric discharge devices connected inanti-parallel for controlling the supply of power from a source to aload, each discharge device having a plurality of principal electrodesand an ignition electrode in contact with one of said principalelectrodes, a full wave rectifier connected between the said controlelectrodes and means associated with said full wave rectifier forcontrolling the flow of ignition current through said ignitionelectrodes.

4. In combination, a pair of electric discharge devices connected inanti-parallel for controlling the supply of power from a source to aload, each discharge device having a plurality of principal electrodesand an ignition electrode in contact with one of said principalelectrodes, a high impedance network connected between said ignitionelectrodes, said network comprising a plurality of rectifiers of the drytype, and means connected across said network for varying the impedanceof said network.

5. In combination, a pair of electric discharge devices connected inanti-parallel for controlling the supply of power from a source ofalternating current to a load, each discharge device having an anode, amercury pool cathode and an ignition electrode in contact with saidcathode, a high impedance network connected between said ignitionelectrodes, said network comprising a plurality of rectifiers of the drytype, means connected across said network for varying the impedance ofsaid network, said means comprising an auxiliary electric dischargedevice and control means for the said discharge device.

6. In combination, a pair of electric discharge devices connected inanti-parallel, each discharge device having a plurality of principalelectrodes and an ignition electrode in contact with one of saidprincipal electrodes, means for impressing an alternating potentialbetween said principal electrodes, a network connected between the saidignition electrodes, the said network comprising a plurality ofrectifiers and means connected across said network for controlling theflow of ignition current through said ignition electrodes.

'7. In combination, a pair of electric discharge devices connected inanti-parallel, each discharge device having a plurality of principalelectrodes and an ignition electrode in contact with one of saidprincipal electrodes, means for impressing an alternating potentialbetween said principal electrodes, a network connected between saidignition electrodes, the said network comprising a plurality ofrectifiers, and means connected across said network for controlling theflow of ignition current through said ignition electrodes, said meanscomprising an auxiliary electric discharge device and timing means forthe said auxiliary discharge device.

8. In combination, a pair of electric discharge devices connected inanti-parallel for controlling the supply of power from a source to aload, each discharge device having a plurality of principal electrodesand an ignition electrode in contact with one of said principalelectrodes, a full wave rectifier connected between the said controlelectrodes and means associated with said full wave rectifier forcontrolling the flow of ignition current through said ignitionelectrodes, the said means including an auxiliary electric dischargedevice and timing means for the said auxiliary discharge device.

9. For use in supplying an alternating current load from a source ofalternating current, the combination comprising a pair of electricdischarge devices of the immersed ignition electrode type connected inanti-parallel between said source and said load, each of said dischargedevices having an anode, a cathode, an ignition electrode immersed insaid cathode, a network comprising a plurality of rectifiers, the saidnetwork having a junction connected to one of said ignition electrodesand another junction connected to the other of said ignition electrodes,and means, including an auxiliary discharge device, for transmittingcurrent through a portion of said network and said ignition electrodesto render one of said discharge devices conductive.

10. For use in supplying an alternating current load from a source ofalternating current, the combination comprising a pair of main electricdischarge devices of the immersed ignition electrode type connected inanti-parallel between said source and said load, each of said maindischarge devices having an anode, a cathode, and an ignition electrodeimmersed in said cathode, a network comprising a plurality ofrectificrs, the said network having a junction connected to one of saidignition electrodes and another junction connected to the other of saidignition electrodes,

an auxiliary electric discharge device connected across the saidnetwork, and control means associated with said auxiliary dischargedevice for controlling the flow of current through the said network andsaid ignition electrodes to render said main discharge devicesconductive.

11. In a system for supplyin alternating current from a source ofalternating current to a load, the combination comprising a pair of electric discharge devices of the immersed-ignitionelectrode type connectedin anti-parallel between said source and said load, each of saiddischarge devices having an anode, a cathode, and an ignition electrodeimmersed in said cathode, a plurality of back-to-back rectifiersconnected between the ignition electrodes of said discharge devices,said rectifiers having a common junction, and means for transmittingcurrent through said rectifiers and said ignition electrodes to rendersaid discharge devices conductive, said means including a singledischarge path connected to the common junction of said rectifiers.

12. For use in supplying an alternating current load from a source ofalternating current, the combination comprising a pair of main electricdischarge devices of the immersed ignition electrode type connected inanti-parallel between said source and said load, each of said maindischarge devices having an anode, a cathode, and an ignition electrodeimmersed in said cathode, a network comprising a plurality ofrectifiers, the said network having a junction between one pair of saidrectifiers connected to one of said ignition electrodes and anotherjunction between another pair of said rectifiers connected to the otherof said ignition electrodes, an auxiliary electric discharge deviceconnected across the said network, and control means associated withsaid auxiliary discharge device for controlling the fiow of current fromsaid source through the said network and said ignition electrodes torender said main discharge devices conductive.

RUSSELL W. STAGG-S.

